The ComboBox is a user interface control item in which user can select any value through multiple presents values and it is working as list box. All The contents of ComboBox can be shown and hidden as the control expands and collapses. In the default state the list is collapsed, displaying only one choice. for example we are daily used shopping cart web sites and in there web site multiple ComboBox regarding selection of multiple objects. The user clicks a button to see the complete list of options. A ComboBox is a user input event button in which the user can select an option from a drop-down list or type in a value into a text box so that the appropriate choice can be selected. By default ComboBox work on single value selection but w can create multiple values selection by using check box.